SPERMATOGENESIS. 



2 7 I 



Stages in the transformation of a spermatid into a spermatozoon are 



shown in the diagram Fig. 307. 



The twelve (?) chromosomes of 



the spermatid disappear in a dense 



chromatic network which becomes 



an apparently homogeneous mass. 



This deeply staining nucleus passes 



to one end of the protoplasm of 



the spermatid and becomes the 



essential part of the head of the 



spermatozoon. In man it is a flat- 

 tened structure, oval on surface 



view, and pyriform with its apex 



forward, when seen on edge (Fig. 



308). The head is at the anterior 



end of the spermatozoon which 



during its development is directed 



toward the basal layers of the 



convoluted tubule. The anterior 



end of the head is probably covered 



by a thin layer of protoplasm, 



known as the galea capitis. The 



archoplasm of the spermatid 



(known as the idiozome) is said to leave the centrosome and to enter 



the protoplasm of the galea capitis where it forms the perforatorium. If 

 this exists in man it is in the form of a cutting edge 

 following the outline of the front of the head; in 

 other animals the perforatorium may be a slender 

 spiral or barbed projection which enables the 

 spermatozoon to penetrate the ovum. 



The protoplasm of the spermatid forms an 

 elongated mass at the posterior end of the nucleus. 

 It contains the centrosome which soon divides in 

 two. Of these the anterior forms a disc which 

 becomes adherent to the nuclear membrane. The 

 posterior centrosome also becomes a disc after giv- 

 ing rise to a motile axial filament which grows out 

 from it like a cilium. The disc-like centrosome 

 attached to the anterior end of the filament 



becomes thin in such a way that its peripheral portion is detached, 



and as a ringjsurrounding the filament it passes to the posterior limit of 



FIG. 307. DIAGRAMS OF THE DEVELOPMENT OF 

 SPERMATOSOA. (After Meves.) 



a. c., anterior centrosome; a. f., axial filament; 

 c. p., connecting piece; ch. p., chief piece; 

 g. c., galea capitis; n., nucleus; nk., neck; p., 

 protoplasm; p. c., posterior centrozome. 



FIG. 308. SPERMATOZOA: i, 

 2, 3, HUMAN; 4, FROM A 

 BULL. 



a, Head; b, connecting piece, 

 and c, chief piece of the 

 tail, i, 2, and 4, Sur- 

 face views; 2, side view. 

 X 360. 



